TFTs generally include a substrate containing an electrically conductive gate electrode, source and drain electrodes, an electrically insulating gate dielectric layer separating the gate electrode from the source and drain electrodes, and a semiconducting layer in contact with the gate dielectric layer and bridging the source and drain electrodes, TFTs are the key elements of integrated circuits (ICs), and the performance of TFTs may be determined by the field effect mobility and the current on/off ratio of the overall transistor. High mobility and high on/off ratios are desired.
Organic thin-film transistors (OTFTs) may be used in applications, such as radio frequency identification (RFID) tags and backplane switching circuits for displays, such as signage, readers, and liquid crystal displays, where high switching speeds and/or high density are not essential. OTFTs also have attractive mechanical properties, such as being physically compact, lightweight, and flexible.
OTFTs may be fabricated using low-cost solution-based patterning and deposition techniques, such as spin coating, solution casting, dip coating, stencil/screen printing, flexography, gravure, offset printing, ink-jet printing, micro-contact printing, and the like. The use of these solution-based processes in fabricating TFT circuits requires solution processable materials. However, organic or polymeric semiconductors formed by solution processing tend to suffer from limited solubility, air sensitivity, and especially low field-effect mobility. This poor performance may be attributable to the poor film-forming nature of small molecules.
Although the last two decades have seen a dramatic increase in mobility for printable organic semiconductors, such as polythiophenes and polythiophene derivatives, there is a continuous need for improving the mobility of semiconductors for broad applications.